The present invention relates to sealing devices in general, and more particularly to improvements in inflatable sealing devices. Still more particularly, the invention relates to improvements in inflatable seals which can establish or terminate a sealing action between two spaces, chambers or other areas which are maintained at different pressures. Typical examples of apparatus wherein the sealing device of the present invention can be put to use are ionography imaging chambers wherein dielectric receptor sheets are provided with latent images of X-rayed objects in an interelectrode gap while the gap is filled with a compressed high Z gas, such as Freon, Xenon or Krypton. During imaging of an object onto the receptor sheet in the interelectrode gap, the gap must be sealed from the surrounding atmosphere in order to prevent escape of high Z gas which is maintained well above atmospheric pressure, e.g., at a pressure of 6 to 20 atmospheres above normal atmospheric pressure.
It is already known to seal the interelectrode gap of an ionography imaging chamber from the surrounding atmosphere by resorting to inflatable elastic sealing devices. For example, German Offenlegungsschrift No. 25 40 404 discloses a hollow cylindrical seal which is inserted into a circumferential groove of one section or member of the housing of the ionography imaging chamber so that it surrounds the interelectrode gap. When the seal is expanded from within, it extends across the adjacent portion of the clearance which connects the interelectrode gap with the atmosphere and engages another section or member of the housing of the imaging chamber to thus prevent escape of the high Z gas which is admitted into the gap as soon as the expansion or inflation of the seal is completed. A drawback of such sealing devices is that they cannot adequately seal a relatively wide clearance, especially if the pressure differential at the opposite sides of the inflated seal is very high. This is due to the fact that the force with which a readily deformable cylindrical hose-like seal engages the surface of the other member of the housing of the imaging chamber is relatively small and also that, when the clearance is rather wide and the pressure differential is pronounced, the readily deformable seal undergoes pronounced deformation under the action of compressed high Z gas. In other words, the mechanical stability of an inflatable cylindrical seal is much too low to insure the establishment of a reliable sealing action in response to admission of highly compressed high Z gas into the gap between the electrodes of the imaging chamber. Moreover, the useful life of the just described seal is short and the interval which is required for its inflation is rather long so that the preparation of the imaging chamber for the making of a latent or visible image of an X-rayed object consumes a substantial amount of time.